Consider adding django-test-migrations

[sobolevn]

I know that django-celery-beat had some issues with migrations back in the days.

I am proposing to add the support of testing migration files to prevent errors like:

1. Inconsistent migrations order, like here: https://github.com/celery/django-celery-beat/blob/master/django_celery_beat/migrations/0006_periodictask_priority.py#L9
2. Possibly incompatible changes to existing models in a complex migrations, like this one: https://github.com/celery/django-celery-beat/blob/master/django_celery_beat/migrations/0010_auto_20190429_0326.py#L22

This can be done with the help of https://github.com/wemake-services/django-test-migrations

I would be glad to hear your feedback if any.

[liquidpele]

I added tests because of those issues, see https://github.com/celery/django-celery-beat/blob/master/t/unit/test_models.py#L14

Also the tox file now does these tests starting from various versions so there's full coverage.

[auvipy]

new migrations tests are added to the project